The function, reliability and performance of semiconductor devices depend on the use of semiconductor materials and surfaces which are clean and uniform. Billions of dollars and countless man-hours have been spent developing, characterizing, and optimizing systems and processes for fabricating and processing semiconductor materials. A primary goal of this activity has been the fabrication of materials and surfaces that are extremely clean and that have predetermined and desired properties that are uniform, vary uniformly or vary in a programmed manner, across the entire wafer. In order to characterize and optimize these processes and the resulting material, it is necessary to be able to inspect and measure surface or bulk cleanliness and uniformity or the precise variation of properties over all the surface. For real-time process control, it is necessary to be able to make many measurements across a surface at high speed, and to do so in a manner that does not damage or contaminate the semiconductor surface.
The technologies available for the inspection of patterned wafers are very limited. The most common methods and systems use optical, or light based technologies to inspect for particles, scratches or other types of physical defects. They operate by illuminating the surface with broadband, narrowband, or laser light, collecting the scattering or reflected light using optics, and acquiring images using photosensors such as Charged Coupled Devices (CCDs), Time Delay Integration (TDI) sensors, or Photo Multiplier Tubes (PMTs). These systems then process these images to detect physical defects such as particles and scratches. Alternatively, e-beam technology can be used by subjecting the wafer to high vacuum, accelerating electrons onto the wafer surface, collecting the scattered electrons from the surface, and acquiring images using scintillators and PMTs. These types of systems are not however able to detect sub-monolayer chemical non-uniformities in, or on, the wafer surface; and are not able to detect pre-existing charge variation across the wafer. Technologies that are capable of detecting small chemical variations are not suitable for the inspection of patterned wafers because they lack the speed or resolution to inspect the whole wafer, are destructive, or are not suitable for use on complex surfaces that include significant material and geometric variations. For example, Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS) is often used to characterize the chemical composition of a surface, but is much too slow to image large areas of a wafer and is primarily used for analysis of one or more points. Such technology is not commercially useful due to these deficiencies. Total Reflection X-ray Fluorescence (TXRF) is often used to detect metals at selected points on the surface of bare or blanket wafers, but lacks the speed and resolution to image patterned wafer surfaces. In addition, the results are confused by the variations in surface chemistry that occur on patterned wafers. In general, these types of non-optical tools are used to characterize test structures or review defects detected by optical tools. However, there is no viable technology for inspecting whole patterned wafers to detect chemical or charging non-uniformities that can significantly impact semiconductor device performance or yield. Consequently, there is a long felt need for a method for rapid and accurate analysis of nonuniformities or defects present on surfaces, such as semiconductor wafers.